The present invention generally relates to sample analyzers, and more particular, to sample analyzers and cartridges that can be used at the point of care of a patient, such as in a doctor's office, in the home, or elsewhere in the field.
Particle discrimination methods are useful in a variety of clinical assays, such as in determining the number and types of cells in a blood sample, detecting bacterial or virus particles in a body fluid sample, and assaying cell volumes and density. Detection of non-cellular particles, such as proteins and analyte in for example, a urine sample, is also valuable in certain clinical tests. Analysis of crystals and other particles in fluid suspension also has important industrial uses.
One method which allows rapid and efficient particle discrimination in a particle-suspension sample is flow cytometry. In this method, a suspension of particles, typically cells in a blood sample, is transported through a flow channel where the individual particles in the sample are illuminated with one or more focused light beams. The interaction of the light beam(s) with the individual particles flowing through the flow channel is detected by one or more light detectors. Commonly, the detectors are designed to measure light absorption or fluorescence emission, at specific beam or emission wavelengths, and/or light scattering at specific scattering angles. Thus, each particle that passes through the flow channel can be characterized as to one or more features related to its absorption, fluorescence, light scattering or other optical or electrical properties. The properties that are measured by the detectors may allow each particle to be mapped into a feature space whose axes are the light intensities or other properties which are measured by the detectors. In the ideal, the different particles in the sample map into distinct and non-overlapping regions of the feature space, allowing each particle to be analyzed based on its mapping in the feature space. Such analysis may include counting, identifying, quantifying (as to one or more physical characteristics) and/or sorting of the particles.
Two general types of light scattering measurements are routinely made in flow cytometry. Light intensity measurements made at small angles (about 1.5-13 degrees with respect to the incident light beam), usually called forward or small-angle scattering, give information on cell size. Forward scattering also strongly depends on the difference of refraction between cells and the extra-cellular medium, so that cells with damaged membranes, for example, can be distinguished. Light intensity measurements made at an angle of about 65 degrees-115 degrees from the incident light, usually referred to as orthogonal or large angle scattering, can provide information about the size and degree of structure of particles.
Simultaneous light scattering measurements at different angles or in combination with absorption or fluorescence measurements have been proposed in flow cytometry methods. For example, absorption of light in combination with light scattering can be used in flow cytometry to distinguish between erythrocytes and thrombocytes, and between lymphocytes, monocytes, basophilic granulocytes, eosinophilic granulocytes, and neutrophilic granulocytes. However, this method sometimes requires staining of the cells, and is therefore rather complex and may preclude using the cells for further study after cell sorting.
Light scattering measurements combined with circular dichroism (CD) and optical rotatory dispersion (ORD) also have the potential for particle discrimination in suspensions of virus particles or cells. Studies of the effect of Mie (isotropic particle) scattering on the CD and ORD spectra of DNA in viral particles suggest that scattering measurements can be used to correct ORD and CD measurements in larger biological structures, such as virus particles and cells, to allow particle discrimination on the basis of characteristic ORD and CD characteristics. Differential scattering of right and left circularly polarized light, for discrimination of a number of different microorganisms, has also been demonstrated. The circular intensity differential scattering (CIDS) method is like CD, which exploits the differential absorption of left and right circularly polarized light, but takes advantage of differential scattering by helical structures, such as DNA, of right and left circularly polarized light.
Typically, such particle discrimination methods are implemented, at least in part, using one or more pieces of equipment, collectively herein called a sample analyzer. Many sample analyzers are rather large devices that are used in a laboratory environment by trained personnel. To use many sample analyzers, a collected sample must first be processed, such as by diluting the sample to a desired level, adding appropriate reagents, centrifuging the sample to provide a desired separation, etc., prior to providing the prepared sample to the sample analyzer. To achieve an accurate result, such sample processing must typically be performed by trained personnel, which can increase the cost and time required to perform the sample analysis.
Many sample analyzers also require operator intervention during the analysis phase, such as requiring additional information input or additional processing of the sample. This can further increase the cost and time required to perform a desired sample analysis. Also, many sample analyzers merely provide raw analysis data as an output, and further calculations and/or interpretation must often be performed by trained personnel to make an appropriate clinical decision.